Regulation of Na+and K+Transport and Oxidative Stress Mitigation Reveal Differential Salt Tolerance of Two Egyptian Maize (Zea maysL.) Hybrids at the Seedling Stage

Maize is sensitive to salinity stress, which has adverse effects on plant growth and yield. In this study, two Egyptian white maize hybrids, single cross 131 (SC131) and single cross 132 (SC132), were exposed to 100 mM NaCl stress for 12 days in a hydroponic culture and physiological and biochemical parameters, and gene expression for some Na(+)and K(+)transporters were evaluated. The results revealed that the total dry weight of SC131 was greater than that of SC132. The root growth was also better for SC131 than SC132. The Na(+)concentration in leaves and stems, and H(2)O(2)were significantly lower in SC131 than in SC132, while the proline concentration was higher in the leaf of SC131 than in SC132 under salt stress. Moreover, catalase and ascorbate peroxidase activities increased with salinity in SC131 leaves compared to catalase and GR in SC132. Salt stress slightly induced the expression ofZmHKT1;5(for Na(+)exclusion) in SC132, but repressed it in SC131. On the other hand, the expression ofZmHKT2gene (for K(+)exclusion) was highly induced by salt stress in SC132, but was not detected in SC131. The salt increased the expression ofZmNHX1(for vacuolar Na(+)sequestration) in SC132, but repressed it in SC131. Taken together, these results suggest that the maize hybrid SC131 is more tolerant to salinity than SC132, thanks to a more efficient leaf Na(+)exclusion mechanism, that is yet to be investigated, and to a better antioxidant defense system. Thus, SC131 could constitute a new hybrid worthy of consideration in maize breeding programs for enhanced productivity on salt-affected soils.